1. Field of the Invention
The present invention relates to a scanner module and an image scanning apparatus employing the scanner module, and, more particularly, to a mounting structure of a light guide in a scanner module.
2. Description of the Related Art
Generally, a scanner module may be employed in an image reading apparatus to read image from a desired portion of a document. To this end, a scanner module may include an illuminator to irradiate light to the portion of the document to be read and a focusing lens to focus the light reflected from the portion of the document on an image sensor.
With recent development of inexpensive high-luminous-intensity white light-emitting diodes, a scanner module employing white light emitting diodes as the light source has been developed.
An illuminator however also needs to have an appropriate light distribution to provide a uniform image output for each pixel. For this reason, a light guide has been used to guide light, irradiated from light emitting diodes, to the desired illuminating position.
An example of an illuminator that employs light emitting diodes and a light guide, is disclosed in U.S. Pat. No. 6,357,903 B1 to Furusawa et al. (“Furusawa”), which was issued on Mar. 19, 2002).
In legacy illuminators, e.g., one described by Furusawa, a light source is provided at one end of an elongated transparent light guide that is mounted in a case by being slid lengthwise into the case. During the lengthwise insertion onto the case, damages to the light guide suffer, e.g., scratches, or the like, which may have adverse effect on the scanning performance. In addition, there is no structure to guide the light guide into the proper mounting position, exacerbating the possibility of damages, and resulting in imprecise assembly.
When light emitting diodes are used as the light source of an illuminator, the luminous intensity may be limited to a predetermined level. While a higher current or voltage is supplied to the light emitting diodes may result in the light emitting diodes producing light with enhanced luminous intensity, the increased power also raises the temperature of the light emitting diodes, and, consequently, may deteriorate the luminous intensity of light actually emitted by the light emitting diodes.
Moreover, it is desirable that an illuminator be easy to assemble so as to allow mass production. A conventional light guide is formed as an elongated transparent member, which is prone to bending or bowing. It is thus also desirable to provide a guide holder that is capable of supporting the light guide while maintaining the light guide straight.
Furthermore, in the above-described conventional illuminator, both ends of the light guide are fixedly supported, causing the light guide to bend or bow along its length when the light guide lengthens due to thermal expansion by heat generated from the light source. These deformation or damages, e.g., bending or scratches, or the like, of the light guide causes variation in characteristics of light emitted therethrough, and adversely affects the scanning performance and/or quality.